Potentiometer contactor



United rates Patent POTENTIOMETER C'ONTACTOR Elias Blanco, Hollywood,Calif., assignor, by mesne assignments, to 'Daystrom, Incorporated,Murray Hill, N.J., a corporation of New Jersey Application August 30,1955, Serial No. 531,523

4 Claims. (Cl. 338-402) This invention relates to electrical contactdevices and particularly to the contact structure for potentiometershaving wire wound resistor elements.

It is well known that in the use of potentiometers, an adjustablecontact is frequently required. With low frequency potentiometers usedin stationary equipment, little difficulty is encountered in providingthe desired contacts between a tap and a resistor, particularly of thewire wound type. However, with high frequency currents, and where thepotentiometer is used in equipment in portable vehicles, such asautomobiles, ships, and airplanes, where the potentiometer is subjectedto shock and vibration, it has been found that the usual type of contactstructure is not entirely reliable.

The present invention is a construction of an adjustable contact elementwhich has been found to be stable and reliable under all operatingconditions, including vibration, temperature changes, etc., and permitswire to wire adjustments in extremely small potentiometers, such as usedin air-borne equipment. It is particularly suitable for making contactwith resistance wires having diameters of the order of 0.0004 inch whereother types of contact elements are cumbersome and uncertain. The formof the element permits a tap to be made to a single turn at a fixedpoint.

To provide these results, the contact element is made with one sharp orknife edge, such as the edge of a triangle, the edge being insertedbetween the turns of a wire wound resistor. To provide the proper degreeof fine accuracy, the triangular contact element is provided withinsulation on at least one side so that only one conducting side is incontact with the resistor element.

The principal object of the invention, therefore, is to facilitate theelectrical contact between a fixed element and an adjustable element.

Another object of the invention is to provide a potentiometer contactwhich is reliable under all conditions of vibration and temperaturechanges.

A further object of the invention is to provide an adjustable contactfor a miniature sized potentiometer which provides a reliable and finelyadjustable contact between the element and the resistor element.

The novel features which are believed to be characteristic of thisinvention, both as to the manner of its organization and the mode of itsoperation, will be better understood from the following description whenread in conjunction with the accompanying drawings, in which:

Fig. 1 is a front view of a contact structure embodying the invention;and

Fig. 2 is a horizontal section taken along the line 2-2 of Fig. 1.

Referring now to the drawings, Fig. 2 shows a cross section of severalturns 5 of a spiral wound resistor sulation 11 thereon. The spiral turnsare separated from one another as they are positioned 1n pre-formed2,896,185 Patented July 21, 1959 ice grooves 12. The slidable contactelement 13, as illustrated, has a triangular electrical conductingcentral body portion 6 and an insulator 7 on two sides thereof, althoughit is to be understood that the insulation may be only on one side, suchas the left side. This permits contact of the electrical conductingportion only at the point 9 with the turn 4 of wire 5. Although thecontact element 13 has been shown as a perfect triangle, it may have anysuitable shape as long as the lower portion is of wedge-likeconfiguration as illustrated.

The contact element 13 is under spring pressure of any suitable type,one type being illustrated in Fig. 1 by a resilient bar or rod 10, bywhich the contact is pressed between adjacent turns with a wedgingaction. It will be noted that the contact element 13 has considerablylarger portions than the diameter of the resistor Wire 5, and theseproportions are important in preventing any change in the contactresistance at the point 9 during vibration. In one construction, thediameter of the resistance wire 5 was of the order of 0.0004 inch, theheight of the contact element 13 was of the order of 0.008 inch, and thethickness of the insulation 7 was of the order of 0.00005 inch. Theseparation between turns was of the order of 0.0001 inch. The insulation7 may be of any suitable dielectric, such as glass or varnish. Althoughthese dimensions were found satisfactory, variations in the relativevalues of the elements may be made if the biased knife-edge with oneinsulated side is always embodied in the con struction.

It has been found that an adjustable contact element such as abovedescribed provides a stability and reliability of contact under extremevibratory conditions and temperature changes.

I claim:

1. An electrical contact structure comprising a contact element having abody portion with a sharp edge, with insulation on at least one side ofsaid edge, the uninsulated side of said edge being adapted to extendbetween adjacent turns of a wire wound resistor element and makeelectrical contact at a point on one of said adjacent turns, saidcontacting element being many times larger than the diameter of saidwire of said resistor element.

2.. An electrical contact structure in accordance with claim 1 in whichthe insulated side of the edge of said contact element makes contactwith the other of said adjacent turns.

3. An electrical contact structure in accordance with claim 1 in whichmeans are provided for pressing said contact member in a 'wedgingdirection between said adjacent turns.

4. The combination in a potentiometer having a wire wound resistorelement with spaced apart turns, an electrical contact structurecomprising a body of electrical conducting material having an edgeportion and insulation on one side thereof cooperating to form arelatively sharp wedge-like element adapted to extend between adjacentturns of said resistor element, said wedgelike element presenting aconducting face for engaging one of said adjacent turns and aninsulating face for engaging the other of said adjacent turns, and meansfor biasing said wedge-like element in a wedging direction between saidadjacent turns, whereby said wedge-like element is forcibly retained ina contact position against displacement under forces due to shock andvibration.

References Cited in the file of this patent UNITED STATES PATENTS RoseAug. 30, 1949 Ward -u Mar. 22, 1955

